Reversible mining machine chain



April 25, 1939.

c. L. BowMAN 2,155,526 v REVERSIBLE- MINING MACHINE CHAIN Filed Dec. l2, 1936 2 Sheets-Sheet l mm1@ LHENTOR' WW Em..

API' 25, 1939- N c. BowMAN 2,155,526

REVERSIBLE MINING MACHINE CHAIN Filed Dec. 12, 1936 2 Sheets-Sheet 2 INVENTOR.

BY Ches Lowman 0MM Patented Apr. 25, 1939 UNITED STATES PATENT oFFlcE Charles L. Bowman, Canton, Ohio, assignor to The Bowdl Company, Canton, Ohio, a corporation of Ohio Application December 12, 1936, Serial No. 115,491

10 Claims.

My invention relates in general to mining machine cutting chains, and more particularly to reversible mining machine cutting chains.

An object of my invention is the provision of a 5 reversible mining machine chain adapted to hold cutting bits in either one of two positions, so that the chain may be operated in either the forward or reverse direction to cut the coal or other material.

Another object of my invention is the provision of a reversible mining machine chain lug having two opposed recesses for holding the cutting bit whereby the chain may be operated either in the forward or reverse direction by positioning the cutting bit in either one of the two opposed recesses.

Another object of my invention is the provision of a reversible mining machine chain lug having two opposed recesses, wherein either one of `the two recesses is adapted to alternately receive a cutting bit or a plug so that the set screws, which hold either the cutting bit or the plug may be tightly turned in so as to prevent them from becoming lost when the mining machine chain is in operation.

Another object of my invention is the provision of preventing the coal dust or other material from collecting in the recesses of the chain lug which hold the cutting bit or the plug, which if allowed to collect, would interfere with the insertion of the cutting bit or plug.

Another object of my invention is the provision of a reversible mining machine chain lug adapted to hold a rhomboidal shaped bit, wherein the chain lug has two opposed recesses for respectively receiving the bits for forward or reverse cutting, each of said recesses having an abutting surface against which the rear face of the bit abuts, the abutting surfaces sloping downwardly and inwardly to form a common bottom for both recesses and to form a substantially large lug portion between, and to give strength to, the two abutting surfaces, with a minimum of longitudinal distance between the cutting points of the bit` and a line passing vertically through the center of the lug.

Another object of my invention is the pro- Vision of a reversible mining machine chain lug having opposed recesses for respectively receiving the bits for forward and reverse cutting, wherein the longitudinal distance between the cutting point of the bit and a vertical line passing through the center of the lug is reduced to a minimum.

5 Another object of my invention is the proivision of a reversible mining machine chain lug having two opposed recesses for respectively receiving the bits for forward o-r reverse cutting, wherein the central lug portion between the opposed recesses constitutes the uppermost part of the lug, and wherein the end portion upon each side of the recesses slopes downwardly from the central lug portion toreduce the radial distance between the pivotal turning point of the lug when going around the end of the cutter bar and each of the upper end corners of the lug.

Another object of my invention is the provision of a double and reversible mining machine chain lug having two sets of opposed recesses for respectively receiving a set of bits for forward and reserve cutting, one of said sets of opposed recesses being positioned upon one side of the longitudinal and vertical center of the chain lug and the other set of opposed recesses beingy positioned upon the other side of the said longitudinal and vertical center of the chain lug.

Another object of my invention is the provision of having one of said sets of opposed recesses positioned farther from the said longitudinal and vertical center of the chain lug than the other of said sets of o-pposed recesses.

Another object of my invention is the provision of opposed surfaces in the bottom of the bit recesses, to prevent the bit from tipping forward upon being inserted, which forward position would allow the bit to drop too far into the recesses and not keep the proper gauge, thus causing difficulty when the set screw is tightened.

Another object of my invention is the provision of a mining machine chain adapted to hold a cutting bit and made up of a plurality of sections, each section comprising three designs of chain lugs arranged in four positions and adapted to hold six cutting bits.

Another object of my invention is the provision of a reversible mining machine chain lug adapted to hold cutting bits for forward and reverse cutting respectively and made up of a plurality of .sections connected reversely to each other, each section comprising three designs of chain lugs arranged in four positions and adapted to hold six cutting bits, each of said lugs having opposed recesses for receiving the bits for forward and reverse cutting respectively.

Another object of my invention is the provision 5c of a reversible double-ended cutting bit of rhomboidal shape in side elevation and having two substantially parallel diamond shaped faces offset relative to each other at a. rhomboidal angle of substantially 20 degrees to make the length of the 55 faces of the cutting bit substantially 2,5 times the perpendicular distance between the rhomboidal end of the bit.

Other objects and a fuller understanding oi' my invention may be had by referring to the following description and claims, taken in combina.- tion with the accompanying drawings, in which like reference characters, designate like parts, and in which:

Figure 1 represents a plan view of a mining machine chain. lug embodying the features of my invention and is shown in operative relation with a mining machine cutter bar;

Figure 2 represents a top view cfa chain lugV embodying the features of my invention and having two opposed bit recesses located substantially in the longitudinal center of the chain lug;

Figure 3 is a top view of a chain lug embodying the features of my invention and having two sets ci opposed bitrecesses, eachset being positioned on opposite's'idesof the longitudinal center of the chain lug;A L Figure 4 is a top view of a chain vlug embodying the features of my invention and having vtwo opposed bitjrec'esses positioned in the outermost part of the chain lug;

Figure 5 showsthetopview of the chain lug shown in Figures 2, 3, and.4 assembled in a chain; I

Figure 6 is a front elevational View of the chain lug Vshown in Figure 3;

Figure '7 is aside elevational view of the chain lug shown in Figures 3 and 6;

Figure 8 is the longitudinalcrosssectional view taken along the line 8 8 o Figure 6;

Figure 9 is a fragmentary and cross-sectional view taken along theline 9--9 of Figure 8;

Figure 10 is a vfront view of a rhomboidal diamond-shaped cutting bitadapted to iit into the recesses of the chain lug;

Figure 11A is a side elevational view. of the rhomboidal diamond-shaped cutting bit shown in Figure 10; and v,

Figure 12 is aview of a small'insert arranged to nt in the unoccupied recess.

In the mining of coal, the coal mining machine is progressively moved along the edge of the vein of coal, as the mining machine cutting chain which is mounted upon the cutter bar cuts a substantially horizontal cleft under the vein of coal. This produced'a shelf which is subsequently broken off by means of explosives or other means. In the actual operation, the'coaly cutting machine may progressively move in one direction along the edge of the coal for a considerable distance, as much as several hundred feet, before the cutting operation is'iinished. Heretofore, the coal mining machine, which is extremely difiicult to move, had to be dragged back to the starting point again, at which place another similar cut was made after the coal previously out rhad been removed. As is clearly obvious, the

labor and troublein moving the heavy coal mining machine back to its starting pointwas rather expensive, as well as entailing a considerable loss of time. However, 'with the present invention, which embodies av reversible mining machine chain lug, the coal-mining machine may out in the reverse direction, so that it is unnecessary to drag the coal miningimachine back to the starting point.

With vreference. to the drawing, I illustrate three designs of chain lugs in Figures 2, 3, and 4, Which are assembled into a mining machine chain that is adapted to move around the cutter bar lugs.

I0 shown in Figure 1. As illustrated, the cutter bar I0 is arranged to be operated in conjunction with a sprocket wheel I2 that is driven by the mining machine. The cutter bar I0 is provided upon its opposite sides and around its ends with a longitudinal groove II into which the lowermost part of the chain lugs slidably move as they are driven by the sprocketwheel I2. The slack in the chain may be adjusted by turning the adjusting screw I3 which varies the position of the rcutter bar I with respect to the driving sprocket wheel I2. The chain lug may be pivotally connected together by suitable chain straps I'I which have registered openings through which a pivot pin I8 passes pivotally connecting the ends of the straps IIfto the ends-of the chain lug. As shown, the chain straps I'I are spaced apart to provide a chain slot to receive the teeth of the driving sprocket Wheel l2.

The three designs of the chain lug which are assembled to make up the entire chain and shown in Figures 2, 3, andfi, respectively, are indicated respectively by thereference characters I4, I5, and I6.: The chain lug I4 has two opposed bit recesses: 23 and 2li for receiving the cutting bit 22, When the cutting chain is arranged to be operatedV in one direction, the bit 22 is inserted in the bit recess 23, and when the chain is arranged to be operated in the reverse direction, the bitis inserted in thebit recess 24.' A set screw 34 is threadably mounted in eachend oi the chain lug to engage the face of the'cutting bit 22 for securely holding it in the bit recesses when the chain is in operation. The bit recesses 23 and 24 areV arranged in substantially the longitudinal center of the chain lug I4.

The chain lug I5 has two sets of opposed recesses 25 and 2l and 26 and 28. When the chain is arranged to be operated in one direction, the cutting bits 22 are positioned in the bit recesses 25 and 2B and when the chain is arranged to be operated in the reverse direction, the cutting bits 22 are inserted in the bit recesses 21 and 28 The set of opposed recesses 25 and 2l are positioned closer to the vertical and longitudinal center of the chain lug I5 than the sets ofopposed bit recesses 26 and 28. I The chain lug I6 has two opposed recesses 29 and 30 which are respectively adapted to receive the cutting bit 22 for either forward or reverse cutting. As illustrated,'the bit recesses 29 and 30 are rpositioned at the outermost edge of the 'chainlug I6.

The mining machine chain when assembled is made upv of a plurality of sections. VAs illustrated in Figure 5, each section comprises the three designs of the chain lugs as illustrated in Figures 2, 3 and 4 and the lugsare arranged in four positions and adapted to hold six cutting bits. In other words, in Figure 5, beginning at the left, a section comprises'the first four chain The first chain lug, beginning at the left, has a cuttingbit positioned in substantially the longitudinal center of the lug, and being the same as illustrated in Figure 2, the second and third chain lugs being the same as shown in Figure 3, but connected reversely to each other, each with two cutting bits offset at an unequal distance from the longitudinal center of the chain lug and the fourth chain lug being the same as that shown in Figure 4 and having a cutting ybit positioned at the outermost edge of the lug. In assembling the entire chain, each section is connected reversely to each other as illustrated in Figure 5. The'reversed chain sectionW is'not iil) completely shown in Figure 5, only the two lugs I5 and I6 being shown at the right hand end of the assembly in Figure 5. The two lugs which are not shown on the reverse section would correspond to the two lugs I4 and I5 shown on the left-hand end of the section shown in Figure 5. When the chain in Figure 5 is moved to the left, the cutting action of the rst section is fromv the center to the outside of the chain, and the cutting action of the reversed section is from' the outside of the chain to the center of the chain. When the chain is operated in the reversed direction, that is to the right in Figure 5, the bits are removed from their present recesses and inserted into the opposite recesses, in which case the cutting action of the right-hand section is from the center to the outside of the chain, and the cutting action of the left-hand section in Figure 5 is from the outside of the chain to the center of the chain. The entire chain is made up of a plurality of these sections, so that the chainsv may be operated either in a forward or a reverse cutting direction.

There is another big advantage of having the lugs I5 with two sets of opposed recesses, in that a large number of bits may be used with a less number of lugs. For instance, a single section comprises four lugs, but carries six cutting bits. In other words, for a certain length of chain, there can be many more bits thanwould be the case when each lug had only one cutting bit. In addition to this advantage, there is another advantage in that the chain may be assembled of three designs of lugs. This clearly reduces the pattern costs and effects a great saving in the manufacturing costs of the chain.

In the construction of the chain lug, it is important that the distance between the cutting point of the cutting bit and a line passing vertically through the chain lug be reduced to a minimum, in order to eliminate as much trouble as possible when the chain lug is passing around the end of the cutter bar as shown upon the right-hand end in Figure 1. In other Words, the distance between the two opposed recesses must be as short as possible in order to keep the overall length of the lug as short as possible. Thus, when two opposed recesses are inserted in a lug, it requires more space than if only one recess were inserted in the lug. If the upper body of the chain lug is too long, the rear .end of the uppermost part of the lug will strike the coal, as indicated by the broken line 56 in Figure l when the chain lug is passing around the righthand end of the cutter bar. Therefore, in my invention, I provide for sloping the ends upon each side of the central portion of the lug. The sloping ends are indicated by the reference character 35. The main idea is to prevent the ends of the chain lug from swinging around and striking the coal as the chain lug passes around the end of the cutter I0. Also, the shorter the distance between the two ends of the uppermost part of the chain lug, the better the chain lug clears the coal when passing around the end of the cutter bar. Therefore, as shown in Figures 7 and 8, I provide for making the distance 55 as short as possible. To this end, the abutting surfaces 46 and 41 of the recesses 25 and 2'I as shown in Figure 8, slope inwardly and downwardly so that the bottom of the two opposed recesses join each other. At the same time, the substantially triangular central lug portion 36 is sufficiently large enough to give strength to the abutting surfaces 46 and 4'I. This results from the fact that the cutting bits are rhomboidal in shape in side elevation. 'Ihe upper rear portion of the two opposed recesses 25 and 2'I are provided respectively with sloping engaging surfaces 48- and 49 which engage the heel of the rhomboidal diamond-shaped bit 22. By this construction, the cutting bit 22 is prevented from coming out of the recesses when the set screws 24 are tightly turned in and engaging the forward face of the cutting bit. As illustrated in Figures 7 and 8, the bottom of the bit recesses are provided with opposed surfaces 32 to prevent the bit from tipping forward upon being inserted, which forward position would allow the b-it to drop too far into the recesses and not keep the proper gauge, and then if the set screw were tightened against the tipped bit, there Awould be a fulcrum action and put undue strain upon the bit. 'Ihe com.- mon bottom of the opposed recesses 25 and 2 terminates into a lateral opening 3'I which extends from one side of the lug to the other. In this manner, any coal dust or other particles which enter the opposed recesses 25 and 2'I is allowed to fall down into the lateral opening and there the dust or other particles may be cleaned out. The description of the opposed recesses 25 and 2'I as shown in Figures 7 and 8 applies in the same manner to the other opposed recesses, and the cross-section of the recesses for each of the lugs are substantially diamond-shaped as indicated by the fragmentary View shown in Figure 9.

The shape of the rhomboidal diamond-shaped bit is shown in Figures 10 and 11 and has a forward face 4I and a rearward face 42, which are substantially parallel and offset to each other at a rhomboidal angle of approximately 20 degrees as indicated by the reference character 43. Accordingly, the length of each of the diamond shaped faces from its cutting end to its heel end, that is the end coinciding with the larger angle of the rhomboid, is substantially 2.5 times theperpendicular distance between the two rhomboidal parallel ends 44 and 45. The purpose of this relatively long diamond shaped face is two-fold. First, the upper cutting end of the diamondshaped face extends suciently far above the upper most central portion 36 of the lug to present a good eifective cutting tool. Secondly, the lower heel portion of the diamond-shaped face extends far enough into the recesses to present a surface against which the set screw 34 may engage. Otherwise, if the rhomboidal angle 43 was very much more than approximately 20 degrees, the length of the diamond-shaped face of the cutting bit would not be long enough, rst, to do effective cutting, and second, to extend suiciently far into the recesses so that it may be engaged by the set screw 34.

The set screw 34 for the unoccupied recesses may be tightly turned in until the head of the set screw engages the end of the chain lug. This prevents the set screw from becoming loose when in operation. Also, as another means for preventing the set screw 34 of the unoccupied recesses from becoming loose, and maybe eventually lost, while in operation, I provide for inserting a lug 52 into the unoccupied recesses. The lower portion of the lug 52 is substantially diamond-shaped and its upper end has an apron 54 which covers substantially the diamond-shaped opening of the recesses. Above the apron 54, there is a small gripping portion having an opening 53 into which the pointed end of a suitable tool may be inserted for moving the lug from the recesses. 'By using the lug 52, the set screws 34 may be tightly turned in against the forward face of the lug 52 to prevent them from be-v coming loose and eventually lost in some cases.

Although I have described my invention with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

I claim as my invention:

l. A reversible mining machine chain lug adapted to hold a rhomboidal shaped bit comprising, in combination, a chain lug having opposed recesses for respectively receiving the bit for forward or reverse cutting, each of said recesses having an abutting surface against which the rear face of the bit abuts, said abutting surfaces sloping downwardly and inwardly to form a common bottom for both recesses and to form a substantially large lug portion between, and to give strength to, the two abutting surfaces with a minimum of longitudinal distance between the cutting point of the bit and a line passing vertically through the center of the lug, and a set screw for each recessto engage the forward face of the bit to hold same therein.

2. A reversible miningY machine chain lug adapted to hold a rhomboidal shaped bit comprising, in combination, a chain lug having opposed recesses for respectively receiving the bit for forward or reverse cutting, each of said recesses having an abutting surface against which the rear face of the bit abuis, said abutting surfaces sloping downwardly and inwardly to form a common bottom for both recesses and to form a substantially large lug portion between, and to give strength to, the two abutting surfaces with a minimum of longitudinal distance between the cutting point of the bit and a line passing vertically through the center of the lug, a set screw for each recess to engage the forward face of the bit to hold same therein, the central lug portion between the opposed recesses constituting the uppermost part of the lug, and the end portion upon each side of the recesses sloping downwardly from the central lug portion to reduce the radial distance between the pivotal turning point of the lug and each of the upper end corners of the lug.

3. A reversible mining machine chain lug adapted to hold a rhomboidal shaped bit comprising, in combination, a chain lug having opposed recesses for respectively receiving the bit for forward or reverse cutting, each of said recesses having an abutting surface against which the rear face of the bit abuts, said abutting surfaces sloping downwardly and inwardly to form a common bottom for both recesses and to form a substantially large lug portion between, and to give strength to, the two abutting surfaces with a minimum of longitudinal distance between the cutting point of the bit and a line passing vertically through the center of the lug, and a set screw for each recess to engage the forward face of the bit to hold same therein, each of the recesses having an upper and rearward engaging bit surface disposed at an outward angle to the abutting surface to hold the bit in the recess.

4. A reversible mining machine chain lug adapted to hold a rhomboidal shaped bit cornprising, in combinatiorna chain lug having opposed recesses for respectively receiving the blt for forward or reverse cutting, each of said recesses having an abutting surface against which the rear face of the bit abuts, said abutting surfaces sloping downwardly and inwardly to form a common bottom for both recesses and to form a substantially large lug portion between, and to give strength to, the two abutting surfaces with a minimum of longitudinal distance between the cutting point of the bit and a line passing vertically through the center of the lug, a set screw for each recess to engage the forward face of the bit to hold same therein, each' of the recesses having an upper and rearward engaging bit surface disposed at an outward angle to the abutting surface to hold the bit in the recess, the central lug portion between the opposed recesses constituting the uppermost part of the lug, and the end portion upon each side of the recesses sloping downwardly from the central lug portion to reduce the radial distance between the pivotal turning point cf the lug and each of the upper end corners of the lug, the bottom of said bit recesses having at their bottoms opposed surfaces to prevent the bit from tipping forward upon being inserted in the said bit recesses and to maintain the proper gauge.

5. A d-ouble and reversible mining machine chain lug adapted to hold rhomboidal shaped bits comprising, in combination, a chain lug having two sets of opposed recesses for respectively receiving a set of bits for forward and reverse cutting, each of said recesses having an abutting surface against which the rear face of the bits abuts, the said abutting surfaces of each set of opposed recesses sloping downwardly and inwardly to form a common bottom for the recesses of each set and to form a substantially large lug portion between, and to give strength to, the abutting surfaces of each set of recesses with a minimum of longitudinal distance between the cutting points of the bits and a line passing vertically through the center of the lug, one of said sets of opposed recesses being positioned upon one side of the longitudinal and vertical center of the chain lug and the said other set of opposed recesses being p-ositioned upon the other side of the said longitudinal and vertical center of the chain lug, and a set screw for each recess to engage the forward face of the bit to hold the same therein.

6. A double and reversible mining machine chain lug adapted to hold rhomboidal shaped bits comprising, in combination, a chain lug having two sets of opposed recesses for respectively receiving a set of bits for forward and reverse cutting, each of said recesses having an abutting surface against which the rear face of the bits abuts, the said abutting surfaces of each set of opposed recesses sloping downwardly and inwardly to form a common bottom for the recesses of each set and to form a substantially large lug portion between, and to give strength to, the abutting surfaces of each set cf recesses with a minimum of longitudinal distance between the cutting points of the bits and a line passing vertically through the center of the lug, one of said sets of opposed recesses being positioned upon one side of the longitudinal and vertical center of the chain lug and the said other set of opposed recesses being positioned upon the other side of the said longitudinal and vertical center of the chain lug, and a set screw for each recess to engage the forward face of the bit to hold the same therein, one of said sets of opposed recesses being positioned farther from the said longitudinal and vertical center of the chain lug than the other said set of opposed recesses.

7. A reversible mining machine chain lug adapted to hold a rhomboidal shaped bit comprising, in combination, a chain lug having opposed recesses for respectively receiving the bit for forward or reverse cutting, each of said recesses having an abutting surface against which the rear face of the bit abuts, said abutting surfaces sloping downwardly and inwardly to form a substantially large lug porti-on between, and to give strength to, the two abutting surfaces with a minimum of longitudinal distance between the cutting point of the bit and a line passing vertically through the center of the lug, and a set screw for each recess to engage the forward face of the bit to hold same therein.

8. A reversible mining machine chain lug adapted to hold a rhomboidal shaped bit com- Iprising, in combination, a chain lug body having opposed recesses for respectively receiving the bit for forward or reverse cutting, each of said recesses having an abutting surface against which the rear face of the bit abuts, said abutting surfaces sloping downwardly and inwardly to form a substantially large lug portion between, and to give strength to, the two abutting surfaces with a minimum' of longitudinal distance between the cutting point of the bit and a line passing vertically through the center of the lug, the portion of the body in rear of the recesses being elevated above the portions of the body in advance of the recesses, the body portion in rear of the recesses constituting a good strong support for the bit, the body portions in advance of the recesses being relatively low ,to clear the surface being cut and having a set screw threadably mounted therein with the end of the set screw entering the recesses at a considerable distance below the uppermost part of the said body portion which is in rear of the recesses, each of the said recesses having an abutting surface sloping downwardly against which the rear portion of the bit engages, the uppermost portion of abutting surface extending forwardly at an angle substantially parallel to the rhomboidal angle of the bit to prevent the bit from coming out of the recesses.

9. 'I'he combination, with a reversible-double ended rhomboidal bit in side elevation and having forward and rearward diamond shaped faces substantially parallel and offset relative to each other at a rhomboidal angle of approximately 2O degrees to make the length of the said cutting faces substantially 2.5 times the perpendicular distance between the rhomboidal ends of the bit, and having a rearward pair of lateral surfaces which diverge downwardly from the top edge, and a forward pair of lateral surfaces which diverge upwardly from the bottom edge and join the rearward pair of downwardly diverging lateral surfaces on substantially the rhomboidal centerline of the bit, of a body portion having a recess for receiving said bit, said recess being open at its top and having deeplateral sides for engaging a substantial part of the bit, the inner surfaces of said recess having a plurality of engaging portions for engaging the bit, one of said engaging portions comprising two spaced upwardly diverging surfaces for engaging the forward pair of upwardly diverging surfaces of the bit, another of said engaging portions comprising a fiat rearward surface extending down-v wardly from a point near the top of the body portion for engaging the flat rearward face of the bit, another of said engaging portions comprising a pair of spaced downwardly diverging surfaces to engage the rearward pair of downwardly diverging surfaces of the bit, another of said engaging portions comprising a sloping engaging portion which extends angularly out from the at rearward engaging portion to engage the top edge of the bit, the said engaging portions being so arranged that the bit can only enter or leave the open top at substantially the rhomboidal angle, and clamping means to engage the forward face of the bit for holding the bit against movement at the rhomboidal angle, the cutting face of the bit presenting a good effective cutting portion above the said body portion and presenting a lower heel portion far enough into the recess against which the clamping means may engage.

10. The combination, with a reversible-double ended rhomboidal bit in side elevation and having forward and rearward diamond shaped faces substantially parallel and offset relative to each other at a rhomboid angle of approximately 20 degrees to make the length of the said cutting faces substantially 2.5 times the perpendicular distance between the rhomboidal ends of the bit, and having a rearward pair of lateral surfaces which diverge downwardly from the top edge, and a forward pair of lateral surfaces which diverge upwardly from the bottom edge and join the rearward pair of downwardly diverging lateral surfaces on substantially the rhomboidal centerline of the bit, of a body portion having a recess for receiving said bit, said recess being open at its top and having deep lateral sides for engaging a substantial part of the bit, the inner surfaces of said recess having a plurality of engaging portions for engaging the bit, one of said engaging portions comprising two spaced upwardly diverging surfaces for engaging the forward pair of upwardly diverging surfaces of the i bit, an-other of said engaging portions comprising a flat rearward surface for engaging the flat rearward face of the bit, another of said engaging portions comprising a pair of spaced downwardly diverging surfaces to engage the rearward pair of downwardly diverging surfaces of the bit, the said engaging portions being so arranged that the bit can only enter or leave the open top at substantially the rhomboidal angle, and clamping means to engage the forward face of the bit for holding the bit against movement at the rhomboidal angle, the cutting face of the bit presenting a good effective cutting portion above the said body portion and presenting a lower heel portion far enough into the recess l agamst which the clamping means may engage. n

CHARLES L. BOWMAN. 

